Electric motors with brushes have conventionally often been used as wiper motors for an automobile. In this kind of electric motor, a plurality of permanent magnets is arranged at equal intervals in the circumferential direction at the inner peripheral surface of a cylindrical yoke, and an armature is rotationally supported inside these permanent magnets. The armature has an armature core in which a plurality of teeth is formed in a radial fashion. A plurality of long slots is formed in the axial direction between the respective teeth, and coils are formed by coiling winding wires between the slots with predetermined intervals by an overlapping winding method. The coils are electrically connected to a commutator which is fitted and fitted to the rotary shaft from the outside so as to be adjacent to the armature core.
The commutator has a plurality of segments, which is metal pieces, arranged in the circumferential direction in a mutually insulated state, and a winding starting end and a winding finishing end of a coil are connected to each segment. Additionally, the segments are connected to brushes, respectively, so as to be capable of sliding contact with the segments, and electric power is supplied to the respective coils via the brushes. Also, a magnetic field is formed in a coil to which electric power is supplied, and a rotary shaft is driven by a magnetic attractive or repulsive force which is generated between the permanent magnets of the yoke.
Here, recently, from necessities of small size and high performance of the wiper motor, there is disclosed a technique for achieving multiple poles in which the number of magnetic poles is 4 (the number of pole pairs is 2) and multiple slots, achieving high performance in a motor, arranging four brushes at equal intervals in the circumferential direction, and making the speed of the motor variable (for example, refer to Patent Document 1).
In the motor of Patent Document 1, the amount of an electric current to be supplied to a coil in each mode of a LOW mode, a MID mode, and a HI mode is changed by changing energization patterns to the four brushes. Through this configuration, the rotational frequency of the motor in each mode can be changed while providing a motor in which the number of magnetic poles is 4, and multiple slots are achieved.